The subject of the present invention is a stable aqueous dispersion comprising one or a number of hydroxylated fluorinated copolymers and optionally one or a number of acrylic copolymers. These dispersions have the advantage of being stable on storage, of being suitable for forming films with excellent adhesion to various substrates, and of having good chemical properties and good mechanical strength. In general they have the additional advantage of possessing a high solids content, that is to say greater than 30% by weight. These dispersions can be used as paints or coatings which can be applied in a number of ways to a variety of substrates.
Aqueous dispersions are described in EP 212,508 and EP 224,870, assigned to Daikin, EP 341,716, assigned to Asahi Glass, and EP 508,229, assigned to Central Glass. All of these dispersions contain an alcohol and a tertiary amine, such as triethylamine. The presence of amine in a paint composition has the disadvantage of leading to yellowing of the paint during the film-forming heat treatment or even the appearance of small holes at the surface of the said paint.
EP 360,575, assigned to JSR, describes solvent-free and amine-free aqueous dispersions in the vinylidene fluoride copolymer latex form prepared as an emulsion and seeded with an acrylic copolymer with a low glass transition temperature; the main defect of these dispersions is their lack of hardness, which is particularly injurious to paint applications.
Fluorinated polymers are known for their chemical resistance, especially to solvents, their excellent thermal behavior and resistance to bad weather and to radiation, for example ultraviolet radiation, their impermeability to gases and to liquids, and their property as electrical insulators. They nevertheless have the disadvantage of being rather difficult to use, in particular for film-forming, with adhesion, transparency, and impact resistance properties which are in general inferior to other thermoplastic polymers such as polyamides.
The present invention provides a stable aqueous dispersion comprising an emulsifying agent and a hydroxylated fluorinated copolymer, wherein said hydroxylated fluorinated copolymer is the result of copolymerization of the following monomers: (a) tetrafluoroethylene, (b) a member selected from the group consisting of vinylidene fluoride, trifluoro-ethylene, and mixtures thereof, and (c) a member selected from the group consisting of allylic alcohol, allylic ethers, and mixtures thereof. The monomers are copolymerized in molar ratios such that (b)=45 to 95% of (a)+(b) and (c)=2 to 25% of (a)+(b). Optionally, the hydroxylated fluorinated copolymer may be the result of copolymerization of monomers (a), (b), and (c), and of (d) a member selected from the group consisting of nonhydroxylated vinyl ethers; fluorinated monomers other than vinylidene fluoride, trifluoroethylene, and tetrafluoroethylene; non-salified allylic ethers and esters which are optionally carboxylated and/or substituted with xe2x80x94(CF2)nxe2x80x94CF3 having 4 less than n greater than 10; and mixtures thereof. In this case, the monomers are copolymerized in molar ratios such that (b)=45 to 95% of (a)+(b), (c)=2 to 25% of (a)+(b), and (d)= greater than 0 to 10% of (a)+(b).
In another aspect of the present invention, the stable aqueous dispersion may further comprise an acrylic copolymer wherein said acrylic copolymer is the result of copolymerization of the following monomers: from 40 to 70% (by mass) of methyl methacrylate; from 30 to 60% (by mass) of an alkyl (meth)acrylate, and from 0 to 15% (by mass) of a functionalized or substituted alkyl (meth)acrylate monomers. The ratio by weight of the acrylic copolymer(s) to the hydroxylated fluorinated copolymer(s) in the stable aqueous dispersion is less than 50%.
The stable aqueous dispersions according to the present invention are preferably characterized by solids contents of at least 30% by weight.
The present invention also contemplates processes for the manufacture of a stable aqueous dispersions. One such process comprises preparing a solution of hydroxylated fluorinated copolymer(s) in an organic solvent, dispersing the solution thus obtained in an aqueous solution of emulsifying agent(s), and removing the organic solvent, either simultaneously by distillation or after dispersion. Another such process comprises copolymerizing the acrylic monomers in the presence of the hydroxylated fluorinated copolymer(s) in solution or in emulsion in an organic solvent, dispersing the solution thus obtained in an aqueous solution of emulsifying agent(s), and removing the organic solvent, either simultaneously by distillation or after dispersion.
The stable aqueous dispersions of the present invention are useful for making aqueous-phase paints and varnishes.
The Hydroxylated Fluorinated Copolymers
The hydroxylated fluorinated copolymers which can be used for the aqueous dispersions according to the invention are known. They are described, for instance, in U.S. Pat. Nos. 5,231,155, 5,166,284, and 5,200,479. They derive from the following monomers:
1. from 45 to 95% (molar) of vinylidene fluoride (VF2) and/or of trifluoroethylene (VF3),
2. from 5 to 55% (molar) of tetrafluoroethylene (C2F4)
3. from 2 to 25 mol, per 100 mol of monomers 1+2, of one or a number of hydroxylated allylic monomers chosen from allylic alcohol and hydroxylated allylic ethers such as
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94CHOHxe2x80x94CH2xe2x80x94OH
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94C(CH2OH)2(CH2CH3) xe2x80x83CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94OH with 3xe2x89xa6nxe2x89xa68
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94(CH2xe2x80x94CH2xe2x80x94O)nxe2x80x94H with 1xe2x89xa6nxe2x89xa614
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94(CH2xe2x80x94CH(CH3)xe2x80x94O)nxe2x80x94H with 1xe2x89xa6nxe2x89xa614
4. and from 0 to 10 mol, per 100 mol of monomers 1+2, of one or a number of monomers chosen from non-hydroxylated vinyl ethers, such as butyl vinyl ether, other fluorinated monomers (i.e., other than VF2, VF3, or C2F4), such as C3F6 or C2F3Cl, or non-salified allylic ethers and esters which are optionally carboxylated and/or substituted with xe2x80x94(CF2)nxe2x80x94CF3 with 4xe2x89xa6nxe2x89xa710, such as:
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94COxe2x80x94C2H4xe2x80x94COOH,
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94COxe2x80x94C6H10xe2x80x94COOH
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94Oxe2x80x94C2H4xe2x80x94(CF2)nCF3,
CH2xe2x95x90CHxe2x80x94CH2xe2x80x94COxe2x80x94Oxe2x80x94C2H4xe2x80x94(CF2)nCF3,
CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94Oxe2x80x94CH2xe2x80x94CF3
The stable aqueous dispersions contain at least 30% by weight of hydroxylated fluorinated copolymer(s).
The Acrylic Copolymers
The acrylic copolymer(s) according to the invention derive from the following monomers:
from 40 to 70% (by weight) of methyl methacrylate (MMA),
from 30 to 60% (by weight) of one or a number of alkyl (meth)acrylate(s), such as butyl acrylate (BuA) or the ethyl (meth)acrylates,
and from 0 to 15% (by weight) of one or a number of alkyl (meth)acrylate monomers which are functionalized or substituted, for example, with hydroxyl groups or CF3xe2x80x94(CF2)nxe2x80x94groups with 4xe2x89xa6nxe2x89xa610, such as hydroxyethyl (meth)acrylate (HEA), 2,2,2-trifluoroethyl methacrylate (TRIFEMA), CH2xe2x95x90CRxe2x80x94COOxe2x80x94C2H4xe2x80x94(CF2)nxe2x80x94CF3 with Rxe2x95x90H or CH3 (CFnA), the (meth)acrylic acids (AA and MAA), the salts of 2-acrylamido-2-methylpropanesulphonic acid, in particular CH2xe2x95x90CHxe2x80x94COxe2x80x94NHxe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94SO3xe2x80x94N+(C2H5)3 (AMPS/TEA), dimethylacrylamide (DMA) or dimethylaminoethyl methacrylate CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94CH2xe2x80x94CH2xe2x80x94N(CH3)2 (MADAME).
The presence of some of the above monomers in the acrylic copolymer(s) improves certain mechanical, physical and/or chemical properties of the dispersion according to the invention. By way of example, hydroxy (meth)acrylates improve the crosslinking properties, TRIFEMA and the (CFnA)s have anti-graffiti properties, acrylic and methacrylic acids improve the adhesion properties, AMPS/TFA and DRA have properties of mechanical stabilization of the dispersion and MADAME makes it possible to coat substrates by cataphoresis.
The ratio by weight of the acrylic copolymer(s) to the hydroxylated fluorinated copolymer(s) and the acrylic copolymer(s) in the stable aqueous dispersion is between 0 and 50% and preferably between 20 and 30%.
Emulsions
The stability of the dispersion is provided for by one or a number of emulsifying agents present in the dispersion. Stable dispersion is understood to mean a dispersion which is stable with time, that is to say which can be used without detrimental change in its properties after prolonged storage, that is, of the order of a few months. The emulsifying agent(s) can be cationic or non-ionic but are preferably anionic. The preferred anionic emulsifiers comprise CF3xe2x80x94(CF2)nxe2x80x94groups with 4xe2x89xa6nxe2x89xa610. Mention may be made, by way of example, of:
CnF(2n+1)xe2x80x94C2H4xe2x80x94SO3xe2x88x92K+ CnF(2n+1)xe2x80x94COOxe2x88x92K+ CnF(2n+1)xe2x80x94COOxe2x88x92NH4+
The stable aqueous dispersions generally contain from 0.5 to 3% of emulsifying agent(s).
Processes
Another subject of the invention is processes for the preparation of stable aqueous dispersions of hydroxylated fluorinated copolymers, on the one hand, and of hydroxylated fluorinated copolymers and of acrylic copolymers, on the other hand.
The literature teaches various methods for the preparation of stable aqueous dispersions. It is possible to attach carboxyl functional groups to the hydroxylated fluorinated polymer chain, either by direct copolymerization or indirectly by chemical reaction of the hydroxyl functional groups. After salification of the carboxylic acid functional groups, aqueous dispersions are obtained. See for example U.S. Pat. Nos. 5,231,155, 5,166,284, and 5,200,479. It is also possible to copolymerize fluorinated olefins with macromers having units derived from ethylene or propylene oxide, as described in EP 341,716. Using the processes set out above with the fluorinated copolymers according to the invention, satisfactory aqueous dispersions, i.e. stable and with a high solids content and free of coagulates, are not obtained.
The process for the preparation of stable aqueous dispersions developed in accordance with the present invention consists in: (a) preparing a solution of hydroxylated fluorinated copolymer(s), optionally in the presence of the acrylic copolymer(s), in an organic solvent, (b) dispersing the solution thus obtained in an aqueous solution of emulsifying agent(s), and (c) removing the organic solvent, either simultaneously by distillation or after dispersion.
The organic solution of hydroxylated fluorinated copolymer(s) alone can in general be obtained by copolymerization of these copolymers directly in solution in the organic solvent. See, for example, U.S. Pat. Nos. 5,231,155, 5,166,284, and 5,200,479. The fluorinated copolymers can be polymerized in solution, in particular in tert-butanol, methyl acetate, or isopropyl acetate. After charging the organic solvent to the polymerization reactor, the hydroxylated allylic monomer(s) and then VF2 and C2F4 are introduced. After having brought the temperature to between 50 and 70xc2x0 C., the polymerization initiator, preferably chosen from isopropyl peroxydicarbonate or tert-butyl peroxypivalate, is added. During polymerization and in order to keep the proportions of the various monomers in constant ratios, VF2, C2F4, and the hydroxylated allylic monomer(s) are added while taking care to keep the pressure constant. When all the monomers have been introduced, the temperature is lowered and the reactor is degassed, the unreacted fluorinated monomers being discharged. If the solvent used during the polymerization of the fluorinated copolymers is an acetate, the organic copolymer solution is suitable for being converted into an aqueous dispersion according to the invention. In contrast, if the solvent used is tert-butanol, it is necessary to carry out a solvent transfer in order to have available fluorinated copolymer in the desired solvent.
In the case of aqueous dispersions also comprising one or a number of acrylic copolymers, it is possible to mix the previously synthesized acrylic copolymer(s) with the solution of hydroxylated fluorinated copolymer(s) or else to copolymerize the acrylic monomers, that is, the monomers from which the acrylic copolymer(s) derive(s), directly in the organic solvent in the presence of hydroxylated fluorinated copolymer(s). The copolymerization of the acrylic copolymers in the solution of hydroxylated fluorinated copolymer(s) can be carried out by adding the entirety or a fraction of the acrylic monomers, which is introduced either continuously or by successive increments during polymerization. The polymerization temperature is in general between 40 and 90xc2x0 C. It is possible to use transfer agents of mercaptan type in order to reduce the molecular masses and organosoluble radical initiators in general chosen from initiators of azo, peroxydicarbonate, peroxypivalate, and diacyl peroxide type. Mention may be made, as example, of azobisisobutyronitrile, cyclohexyl peroxydicarbonate, or tert-butyl peroxypivalate.
In the case of the aqueous dispersions also comprising one or a number of acrylic copolymers, a variant consists in using the seeded emulsion polymerization technique, such as described in EP 320,126 and EP 360,575, which consists in carrying out an emulsion polymerization of the mixture of acrylic monomers in the presence of hydroxylated fluorinated copolymer latex/latices or of an artificial dispersion of hydroxylated fluorinated copolymer(s).
The organic solvents according to the invention have a boiling point in general of between 30 and 90xc2x0 C. and a solubility in water of in general between 0.5 and 500 g/l (measured at 20xc2x0 C., NTP conditions). Mention may be made of alcohols or esters, the latter being particularly preferred. As an example of preferred solvent, it is possible to use alkyl acetates (methyl acetate, ethyl acetate, and isopropyl acetate, and the like).
The concentration by weight of the hydroxylated fluorinated copolymer(s) in the organic solvent is in general between 15 and 40%.
Dispersion of the copolymers can be carried out using dispersers or homogenizers capable of dispelling a great deal of mechanical energy into the mixtures of immiscible liquids. These devices make it possible to produce emulsions of xe2x80x9coil-in-waterxe2x80x9d type by virtue of the addition of appropriate emulsifying agent(s), the xe2x80x9coilxe2x80x9d phase being in this instance the organic solution of hydroxylated fluorinated copolymer(s). The aqueous solution/copolymer solution mixture is subjected to intense shearing by a mechanical stirring system or else by passing under pressure through nozzles. In general, the dispersion stage can be carried out within a temperature range of between 0 and 100xc2x0 C. and preferably between 15 and 50xc2x0 C.
The water/copolymer solution ratio by weight is in general between 0.2 and 1.
Properties and Use
After removal of the organic solvent, an aqueous dispersion is obtained which is stable on prolonged storage and which can be used several months after its manufacture without lessening of its properties. The mechanical stability on storage of the aqueous dispersion can be assessed by carrying out, on the one hand, a sedimentation test and, on the other hand, by measuring the size of the dispersed particles.
The sedimentation test consists in leaving the dispersion to stand for a month and in then evaluating any deposit formed after brief stirring followed by standing for 24 hours. The ratio by weight of deposited and dried copolymers to the total amount of dried copolymers present is calculated.
The size of the particles is measured by analysis of the scattering of a monochromatic beam through a dilute sample of the dispersion.
Another subject of the invention is the use of the aqueous dispersions as binders for water paints. Water paints have become widely used in recent years due in particular to their ease of use (light equipment not requiring a system for removing the solvents, easy cleaning of the equipment) and to a collective awareness of the problems of pollution of the environment. While the base constituents of paints, such as fluorinated polymers and acrylic polymers, are often soluble in organic solvents of ester or ketone type, they are in general insoluble or virtually insoluble in water. There has therefore been a search to emulsify or disperse these essential constituents of paints so as to be able to use them in the aqueous phase.
In addition to the dispersions according to the invention, aqueous-phase paint binders comprise one or a number of hardeners which are in general resins carrying functional groups capable of chemically reacting with the hydroxyl groups of the dispersed copolymers. Mention may be made, among hardeners which can be used in the context of the invention, of blocked or free polyisocyanate resins, it being necessary for the latter to be subjected to a pretreatment which makes it possible for them to be emulsified in water, or melamine/formaldehyde or urea/formaldehyde resins.
The paints can also contain one or a number of pigments which can be of inorganic or organic type. It is preferable, in general, to use inorganic pigments, among which mention may be made of titanium dioxide, iron or chromium oxides, mixed cobalt and aluminum oxides, carbon black, molybdate orange, corrosion-inhibitor pigments, such as zinc phosphate, or metallic pigments, such as aluminum.
The aqueous paints can also contain a small amount of solvent for the hydroxylated fluorinated copolymer(s), in order to improve the film formation thereof. Mention may be made, as example, of alcohols, ethers or ethers of glycol or of propylene glycol.
It is also possible to add, to the paint, any conventional adjuvant or additive for varnishes and paints, such as dispersing agents, thickeners of associative or non-associative type, agents intended to promote spreading, rheology-modifying agents, heat-stabilizing and/or ultraviolet-stabilizing agents, antioxidants, anti-foaming agents, wetting agents for pigments and/or vehicles, fungicides, bactericides, antifreezes, catalysts of the hardening reaction of the paint, and the like.
The paint is prepared in a way known per se by mixing the various constituents. In general, the pigment(s) is/are dispersed in water, in the optional presence of dispersant(s), and then mixing is carried out at high speed until a dispersion having the required fineness is obtained. The preparation can be carried out in a disperser-type device where the liquids to be mixed are subjected to a high degree of shearing due to the intense stirring (Ultra-Turrax(copyright) device). It is also possible to obtain shearing by pumping the mixture of liquids to be dispersed through calibrated nozzles (Manton-Gaulin device). It is also possible to disperse the liquids efficiently in an ultrasonic vessel of high frequency. Mention may also be made of electric dispersers where one of the phases to be dispersed is passed through a capillary placed in an electric field which disperses it in the form of fine droplets. The additive(s) listed above is/are then introduced with stirring, followed by the stable aqueous dispersion. Depending on the nature of the hardener, it is added either at the end of mixing or immediately before use of the paint. When the hardener, for example a polyisocyanate, is introduced at the end of mixing, it is preferable to disperse it beforehand in water before introducing it into the mixture, in order to provide it with a better subsequent distribution in the mixture. The predispersion of the hardener is further improved by diluting it beforehand in a solvent so as to decrease the viscosity and promote emulsification. Mention may be made, among the solvents which can be used, of esters, ether esters or aromatic compounds. Solvents of low solubility are preferred because they are, in general, less liable to destabilize the emulsion of fluorinated copolymers. Solvent of low solubility in water is understood to mean solvents whose solubility in water is less than 30% by weight.
The paints according to the invention can be applied to the substrates to be coated according to any known technique such as compressed-air spray gun, electrostatic, brush, roller, by curtain-coating, by dipping, or by electrodeposition.
The substrates to be coated can be metals, such as steel, galvanized steel, aluminum, and the like, plastics, such as poly(vinyl chloride), polyesters, or phenolic resins, glass, ceramics, wood or concrete. Said substrates may optionally be coated with primer and/or be subjected to a surface treatment intended to promote adhesion of the paint.